1. Field of the Invention
The present invention relates to manufacturing integrated circuits packages. More specifically, the invention relates to aligning a spacer to a silicon die.
2. Description of the Related Art
Digital circuits, no matter how complex, are composed of a small group of identical building blocks. These blocks can be gates or special circuits or other structures for which gates are less suitable. But the majority of digital circuits are composed of gates or combinations of gates. Gates are combinations of high-speed electronic switches, such as transistors.
A microprocessor is a central processing unit of a computer or other device using thousands (or millions) of gates, flip-flops and memory cells. Flip-flops and memory cells are modified versions of basic logic gates.
It is known to manufacture an integrated circuit using conductors separated by a semiconductor. Circuits are fabricated on a semiconductor by selectively altering the conductivity of the semiconductor material. Various conductivity levels correspond to elements of a transistor, diode, resistor, or small capacitor. Individual components such as transistors, diodes, resistors, and small capacitors are formed on small chips of silicon. These individual components are interconnected by wiring patterns (typically aluminum, copper or gold).
An integrated circuit is then included in a larger structure, known as integrated circuit package, that provides electrical connections between the integrated circuit and the next level assembly. The integrated circuit package also serves structural functions. Integrated circuit packages are then mounted on printed (or wired) circuit boards, which are used to assemble electronic systems such as personal computers and other data processing equipment.
It is known to manufacture an integrated circuit package using a layer of silicon and a layer of a substrate. The substrate layer can be ceramic or another material with the necessary electrical insulating properties, such as a ceramic. Heat is applied during the manufacturing process to bond the silicon layer to the substrate layer. Uneven cooling of the silicon and substrate layers (sometimes referred to as the xe2x80x9cpackagexe2x80x9d) could produce failures in the package. Uniform cooling minimizes the number of failures in the package.
After bonding the silicon layer to the substrate layer a heat spreader (sometimes referred to as a xe2x80x9cthermal lidxe2x80x9d or simply a xe2x80x9clidxe2x80x9d) is attached to the package. The thermal lid serves to conduct heat from the integrated circuit package to the environment and thus facilitates even cooling. The lid is typically formed from a metal due to the high thermal conductivity of metals. Typically, neither the thermal lid nor the silicon surface is sufficiently flat to provide an efficient heat exchange interface. Thus, imperfections in the surface of the thermal lid and the surface of the silicon prevent complete surface contact between the surface of the silicon and the surface of the thermal lid. The incomplete surface contact is an impediment to heat transfer, which in turn causes failures of the package.
The lid can be used in conjunction with a heat sink. The heat sink is provided with fins or other external surfaces to increase contact with ambient air. The increased contact with the ambient air further facilitates heat transfer.
The lid also serves to promote even transfer of forces to the package. Even transfer of force to the package prevents force concentrations on the silicon layer, substrate or in some circumstances the printed circuit board. Even force transfer also reduces failures of the package.
To facilitate surface contact between the thermal lid and the silicon surface a thermal interface material (sometimes referred to as a xe2x80x9cdie interface materialxe2x80x9d) is employed. The die interface material can be applied to the surface of the silicon before the thermal lid is attached. The die interface material is not necessarily a solid and can conform to imperfections in the surface of the silicon. Similarly, the die interface material can conform to imperfections in the surface of the thermal lid. Thus, using a die interface material increases the surface contact between the silicon and the thermal lid and promotes heat transfer.
An example of a material that is suitable for a thermal interface material is manufactured by Thermagon of Cleveland, Ohio. This specific material, referred to as T-lma-60, has suitable thermal conductive properties and can be used as a thermal interface material. T-lma-60 can have more than one layer and is a thermal conductive structure phase change material. T-lma-60 changes phase from solid to liquid at approximately 60xc2x0 C. A thermal interface material, such as T-lma-60 or other, can have a plurality of layers. For example, a thermal interface material such as T-lma-60 can have three layers, one of which can be a metallic central layer.
The increased surface contact between the silicon surface and lid has an additional benefit. When the lid is applied to the silicon layer a force is transferred. If the force is not uniformly transferred, failures of the silicon can result. Failures of the silicon surface can result in rejected packages or later failures.
When a heat sink is employed it is also known to utilize a heat sink interface material. Similar in material characteristic to a die interface material, a heat sink interface material is not necessarily a solid. Similar in function to a die interface material, a heat sink interface material also improves heat transfer properties by improving surface contact between the heat sink and the lid. Similar to the die interface material the heat sink interface material improves force transfer by increasing surface contact between the heat sink and the lid.
FIG. 1A depicts substrate 120 adjacent to printed circuit board (sometimes referred to as xe2x80x9cpcbxe2x80x9d) 110. Silicon die 130 is bonded to substrate 120 as previously discussed. Die interface material 150 is a non-solid used to facilitate heat transfer between silicon die 130 and lid 140. Lid 140 contacts heat sink interface material 160 as shown. Heat sink interface material 160 contacts heat sink 170 as shown. Lid interface material 180 is used to facilitate heat transfer between silicon die 130 and substrate 120. FIG. 1B depicts a thermal lid with a cavity depth of zero. As depicted in FIG. 1B, lid interface material 180 is not typically used for applications having a zero cavity thermal lid due to the lack of surface contact between thermal lid 140 and substrate 120.
FIG. 1C also depicts the related art of facilitating heat transfer from a silicon die. As shown in FIG. 1C, die interface material 150 is again employed. However, in the application as depicted in FIG. 1C neither a thermal lid nor a heat sink interface material are employed (as shown previously in FIG. 1B). Still referring to FIG. 1C, die interface material 150 is employed to improve the surface contact between silicon die 130 and heat sink 170. In the application shown in FIG. 1C the heat sink 170 directly contacts die interface material 150.
FIG. 2A depicts the logical steps of placing die interface material 150 on silicon die 130. As shown in FIG. 2A, the method begins with start 210. From start 210 the logical steps include providing substrate, providing silicon die 220 and providing thermal lid 240. After providing silicon die 220 and providing substrate 230 the silicon die 130 and substrate 120 are bonded, 250. Provide thermal lid 240 is shown occurring prior to bonding (250) silicon die 130 to substrate 120 but can occur later. After providing thermal lid 240 die interface material 150 is placed (260) on silicon die 130. After die interface material 150 is place (260) on silicon die 130 thermal lid 140 is placed (270) on die interface material 150. In one method, after the thermal lid and organic thermal interface material are placed on the silicon layer 270, the process ends 295.
Another embodiment is represented in FIG. 2B. In the embodiment represented in FIG. 2B, heat sink 170 is provided, 255. When a heat sink is provided heat sink interface material 160 is also provided, 265. As shown in FIG. 2B, heat sink interface material 160 is placed (280) on thermal lid 140 after the thermal lid is placed (270) on the silicon die. As further shown in FIG. 2B, heat sink 170 is placed (290) on thermal interface material 160 after heat sink interface material 160 is placed (280) on the thermal lid.
Although FIG. 2B depicts providing heat sink 170 and heat sink interface material 160 after bonding (250) heat sink 170 and heat sink interface material 160 can be provided earlier or later in the process. For example, referring to FIG. 2C, providing heat sink 255 and providing the heat sink interface material 265 occur after placing (260) die interface material on silicon die.
FIG. 2D depicts use of a heat sink, without using a thermal lid. Thus, providing a thermal lid (step 240) and providing heat sink interface material (step 265) are not shown. As shown previously (refer to FIG. 2C) providing substrate 230, providing silicon die 220 and providing heat sink 255 are again shown. From providing silicon die 220 the method can proceed to bonding silicon die and substrate, 250. As previously shown (refer to FIG. 2C) the method can proceed from bonding silicon die and substrate 250 to placing die interface material on silicon die, 260. After the die interface material is placed on the silicon die (260) the method can proceed to placing heat sink on the die interface, 295. In application shown in FIG. 2D, a heat sink is used to facilitate heat transfer, but a thermal lid is not used.
The following components contribute to the total thermal resistance of the package: heat sink, heat sink interface material, thermal lid, die interface material, silicon die and substrate. Thus heat transfer is constrained by the number of components and the thermal conductivity and physical characteristics (such as thickness) of those components. What is needed is a method of improving the thermal resistance of the package.
In accordance with the present invention, a method is described which facilitates heat transfer from a silicon die after the silicon die is bonded to a substrate. An alignment tool is used to align the spacer with the silicon die. A thermal conductor (such as a thermal lid or heat sink) is placed on the silicon layer after the silicon layer has been bonded to the substrate layer. A die interface material is not necessarily applied between the silicon die and the thermal conductor. A spacer is used between the substrate and the thermal conductor. The spacer can facilitate heat transfer from the die. The spacer facilitates force transfer from the thermal to the die. The spacer can allow a thermal conductor to be affixed to the silicon die without use of a die interface material. An alignment tool is used to align the spacer with the silicon die.
The specification also teaches an integrated circuit package manufactured by the method taught. The specification also teaches a computer system including an integrated circuit package manufactured by the method taught. The specification also teaches a computer system including an integrated circuit package manufactured by the method taught.
The foregoing is a summary and this contains, by necessity, simplifications, generalizations and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting.